If you read the back story of Diablo, Brevik was definitely involved in the decisions one would typically attribute to one credited with creating the game, it was certainly a team effort so he definitely wasn’t the only creator. Keep in mind this was a different time and everyone was generally expected to wear more hats back then and blizzard north wasn’t that big of a company at that time regardless.

Particularly he had a lot of experience with the rogues which heavily inspired the original Diablo. Because of this he was initially opposed to making the game real-time as opposed to the traditional turn based, enemies only move when you do rogue style.

However as he tells the story he programmed real time movement in a few hours on a Friday night just to see what it would be like. When he tried it out for the first time and clicked the mouse; almost magically the warrior walked over and smashed a skeleton into a pile of bones.

He was convinced right then that real-time was the right choice.

That moment may have been the birth of the ARPG genre.